Unfortunately, a significant number of individuals suffer from decreased kidney function. If the kidney function is depreciated enough, usually to approximately 10% of normal levels, an individual must either undergo kidney dialysis procedures or receive a kidney transplant. Dialysis procedures remove toxic substances, waste, and bodily fluids from the bloodstream when the kidneys are unable to do so. Presently, two types of dialysis are commonly utilized, peritoneal dialysis and hemodialysis.
Peritoneal dialysis generally involves injecting special solutions into the abdomen of a patient through a port, or plastic tube. The special solution enters the abdomen and occupies the space around the abdominal organs known as the peritoneal cavity. Wastes, toxins, and excess bodily fluids mix with the special solution and are retained therein through osmosis. Once the special solution absorbs a sufficient amount of the wastes, toxins, and excess fluids, the combination may be drained out through the port. This process can either occur every four to six hours in a manual procedure, or continuously if used in conjunction with a cycler machine. While this procedure may usually be performed at home by the patient, it will be appreciated that such a process creates a great burden on the patient, and typically interferes with normal life functioning.
Hemodialysis is conducted by circulating blood through an external filtering machine. Typically, a patient will require hemodialysis three-times per week, with each session lasting approximately four hours.
In hemodialysis, an “arterial” catheter removes blood from the body. The blood is then pumped across a semi-permeable membrane containing solutions to remove toxins, wastes, and excess bodily fluids. The cleansed blood is then returned to the body through a “venous” catheter. Other than in emergency situations, dialysis access is generally obtained through an AV fistula or AV graft. The same graft serves to both supply blood to the hemodialysis machine as well as return blood to the body. In this regard, two catheters are typically placed into the AV fistula or AV graft. The catheter closest to the heart typically serves as the “arterial” catheter, flowing blood from the body, and the downstream catheter typically serves as the “venous” catheter, returning blood to the body. Because the pressure gradient between the two needles is typically not great, the hemodialysis machine must include a pump to circulate the blood.
Because, peripheral veins are typically too small in diameter to permit the required flow of 250 milliliters of blood per minute back into the body, AV fistulas are surgically created approximately six weeks before hemodialysis begins in order to artificially enlarge a vein. This is done by joining a vein to an artery in a localized area while the patient is under anesthesia. The increased blood from the artery causes the vein to enlarge and thicken, thus permitting larger flows through the vein then would otherwise be possible. After the six weeks that the fistula needs to heal, two dialysis needles may be placed within the enlarged and thickened vein. One needle permits blood to be removed for dialysis and the other permits cleansed blood to return to the enlarged and thickened vein.
For individuals whose veins are not suitable for an AV fistula, an AV graft may be used. This procedure involves surgically grafting a portion of the patient's saphenous vein, a donor animal artery, or a synthetic conduit and using it to connect an artery to an existing vein. The grafted vein or prosthetic conduit may be double punctured to draw blood into the dialysis machine and return cleansed blood into the body.
Neither AV fistulas nor AV grafts are ideal. The resulting increased blood through the veins may cause a neo-intimal hyperplasia, which could occlude the veins and lead to access loss. Additionally, the direct flow of blood from an artery into the veins puts undue strain on the local vascular system in general, and the heart in particular. Finally, because blood is both withdrawn from and returned to the body in the same AV fistula, dialysis is typically inefficient because of the phenomenon of recirculation.
Recent dialysis advances involve the implanting of dialysis access ports beneath the skin. These ports generally contain a chamber plugged with a self-sealing material, such as rubberized silicone, with a synthetic catheter extending out from within the chamber. The port is placed under the skin and the catheter is surgically implanted into a vein. A second port can similarly implanted beneath the skin and its catheter is surgically implanted into another portion of the vein. In the case of one of these ports, the vein cannulated with both catheters was the Superior Vena Cava. One port may then be used to remove blood for dialysis while the other port is used to return the cleansed blood back to the body.
Unfortunately, even with the use of AV fistulas, AV grafts, and implanted access ports, positioning of the end of the access needle into the artery of the patient can be problematic. As a result, punctures to the artery walls and to portions of the fistulas, grafts, and access ports can occur and result in damage to the structure, which can require additional procedures to replace the damaged structure. Up to 50% of AV fistulas never mature sufficiently to be safely punctured and used as the primary access for hemodialysis. AV grafts readily develop stenoses and clots and require expensive treatments to restore patency and ports because of the designed method of use cause skin tracts to form, which lead to life threatening infections.